Localizer beacon system



April 22, 1952 s. B. PlcKLEs ET AL LOCALIZER BEACON SYSTEM 2 SHEETS-SHEET l Filed Feb. 6, 1948 UMUSQU TTORNEY April 22, 1952 s. B. PlcKLEs ETAL 2,593,435

LOCALIZER BEACON SYSTEM Filed Feb. 5, 1948 2 SHEETSSHEET 2 INVENTORS s/o/vfy P/c/rs .cf/fern? www ATTORNEY Patented Apr. 22, 1952 UNITED STATES PATENT OFFICE LOCALIZER BEACON SYSTEM Delaware Application February 6, 1948, Serial No. 6,638

13 Claims.

This invention relates to navigation systems, and more particularly to an arrangement for guiding a mobile craft lrelative to an electromagnetically defined energy reference zone or line.

Previous instrument landing systems of the radiant energy beam type have required that1the 5 ing on a frequency below 600 megacycles per secradio beacon or localizer transmitter be installed ond become too large in size if they are electriat the far end of the runway. Present advancecally efficient, while if they are aero-dynamically ments in the fields of aviation require the use of sound, they have to be so close to the skin of the longer runways and clearer approaches, which airplane that they receive best from angles conmeans that the single type localizer has'to be siderably above the horizontal. Also, lower frelocated from one to. two miles from the aircrafts quencies more or less prevent the use of slot type point of contact with the runway upon landing. antennae since the apertures required are too Under these conditions, the continued use of the, large. Frequencies considerably above 1,000 previous type localizers results in indications megacycles per secondrequire heavier receiving which are not as accurate as desired, unless the equipment and introduce much greater difficulty localizer course is made sharper. However, las insofar as securing crystal controlled stability is the course is made sharper, the accuracy of Ya concerned.` Y course alignment with respect to the center line As previously mentioned, localizer arrangeof the runway becomes unduly critical. ments which operate from the far end of the It is therefore an object of this invention to runway suffer the disadvantage, that a very high provide an improved arrangement for providing degree of angular definition is required to accuradiation patterns for the guidance of craft along rately place the aircraft in the center of the runa prescribed course. way. Also a very small misalignment of the In accordance with an embodiment of our in- '25 course at the far end will place the course comvention, a localizer arrangement is diwided into pletely off the runway at the approach end. For two units which are installed one on each side of safe routine automatic landings, it is considered the runway in the vicinity of the point of contact that a localizer system should be able to place the for transmitting radiant energy dening the aircraft in the center of the runway with a spread localizer course formed by sub-carrier frequency of not much more than 15 feet. ThisV would call modulation of carrier frequency waves. The v for an angular accuracy at the far end of the spacing between the units is made a desired fracrunway of better than .086 degree under all contion of a wavelength at the sub-carrier frequency ditions. This is an extremely close tolerance for t0 produce the Course guiding zone. any radio antenna system to maintain. On the The above mentioned and other features and other hand, if the localizer equipment is moved objects of this invention will become more apparcloser to the point of contact, then the necessary ent, and the invention itself, though not neceshigh linear definition can be realized with a much sarily dened by the said features and objects, more practical tolerance on angular accuracy. will be best understood by reference to the fol- As shown in Fig. 1 the distance of the antenna IOWHg description 0f an embodmnt 0f the in* 40 arrays I and 2 from the runway is not particuvention taken in connection with the accompanylai-1y critical and preferably may be between 400 ing drawings wherein: and 1000 feet dependent upon the selection of the Fig. 1 illustrates in schematic form a localiser sub-carrier energy frequency. If the antennae arrangement in accordance with the present' inare"y energized with energy of a frequency in the vention. y f 45 vicinity of 1,000 megacycles per second, the re- Fig. 2 shows in block diagram form a circuit arsulting radiation patterns for the' antenna spacrangement for producing radiant energy pattern- S ings mentioned would result in multi-null direcin accordance with the invention. v tivity patterns. However, it is desirablethat the According to Fig. 1 the localizer antenna sys,` maximum energy be radiated parallel tolthe runstem comprises two arrays, I and 2, preferably way in the direction of approach in orderjto prohorizontally polarizedlocated symmetrically, on

2 each side of a runway 3 near the point or region of contact of an aircraft upon landing. Preferably, the antennae are operated over a wide frequency range, as for example. between 600 and 1000 megacycles per second. Antennae operat- Yide' at the, aircraft the maximumof direct signal, and a minimum of signal reflected from field objects in the vicinity of the ground equipment.

In accordance with the invention, the localizer course is formed not by interference of the 1000 megacycles per second energy but by interference in the receiver detector of sub-carrier energy which is impressed upon the 1000 megacycle per second energy. The separation of the two arrays is made preferably a half wavelength at the subcarrier frequency in'order to provide the desired two major lobes 4 and 5 directed down the runway as shown. Carrier signals may be supplied to the two arrays from a common source, and with carefully controlled phase relationship. The 1000 megacycles per second energy may be supplied to the two arrays from circuits of slightly different frequencies in order that no interference patterns of 1000 megacycles per second will exist. As a result of this arrangement, it is possible, as an approximation, to consider that the localizer course is formed as though the sub-carrier waves which preferably should have frequencies in the vicinity of a megacycle per second, are being radiated directly from the antennae. The subcarrier signals thus interfere to form the total or complete side band patterns, which are characterized by different low modulation frequencies as will be explained later. The total side band type patterns are applicable only at distances from the stations large compared with the spacing between the two localizer arrays. Very close to the runway, and between the localizer arrays, the formation of the total side band patterns approximate a family of hyperbolas. Each hyperbola represents, of course, a given difference in the phases of the sub-carrier signals received from the two transmitting arrays. As a result of this hyperbolic characteristic, the course will have nearly straight sides in the critical region close to the point of contact rather than coming to the apex of a sharp pointed V, common to standard localizers. This is a most desirable characteristic for both human and automatic pilots. Since the 1000 megacycle per second arrays may produce patterns having a strong forward lobe, with relatively little radiation to the sides and rear, the signals are received at a maximum distance in the approach direction. However, suicient signals are radiated in all other directions to provide proper indications in an aircraft circling the field at a radius of substantially two miles.

The components of the transmitter proper, as shown in Fig. 2, comprise a crystal oscillator 6 which is used to insure the frequency stability of the 1000 megacycle per second carrier frequency. Two chains of harmonic multipliers 1, 8 and 9 and I0, II and I2, both controlled by the crystal oscillator 6 are used to feed the final 1000 megacycle multipliers such as I3 and I4, respectively. In order to prevent the formation of a 1000 megacycle interference pattern from the two transmitters, an arrangement, such as a rotating condenser I is applied across a frequency determining circuit of the frequency multiplier I in one of the chains. This condenser is made sufficiently large to produce a slight shift in phase with no appreciable detuning effect. This phase shift is carried through the multiplier chain and results in a continuously changing phase between the two 1000 megacycle outputs, thereby prohibiting the formation of a 1000 megacycle interference pattern.

the sub-carriers to identify each of the side band patterns. For course stability, the relative values of fI and f2 should be maintained constant. This may be achieved by providing, for example, two R-C oscillators I6 and I'I so chosen so that the difference in frequency of their waves will be equal to ,fl and their sum to f2. The R-C oscillator outputs are mixed in the mixer circuit I8 and amplified. The mixing action produces components of fl and f2 which are separated in filter circuits I9 and 2IJ and adjusted to be equal by suitable means such as a loss network in one filter. If the level of either of the R-C oscillator changes, it will produce equal variations in the magnitudes of fl and f2 with no resultant course shift.

The modulating frequency outputs fI and f2 are fed into opposite terminals of a low frequency bridge 2I. This bridge may consist of a hybrid coil or its electrical equivalent. Amplifier-modulators 22 and 23 are connected to the output terminals of the low frequency bridge to amplify the mixed modulating frequencies. .Amplifier-modulator 22 will receive equal magnitudes of fl and f2, both in their original phases. The amplified signal then modulates the subcarrier amplifier 24. Amplifier modulator 23 on the other hand receives equal magnitudes of fl, but f2 reversed from its original phase, which signal is then used to modulate the sub-carrier side band generator 25. amplifier and the side band generator are excited by the common crystal controlled subcarrier frequency source 25. The tank circuit in the sub-carrier amplifier 24 and side band generator 25 are detuned suiciently to produce a 45 degree phase shift in opposite directions. This 45 degree phase shift may be either leading in the amplifier and lagging in the side band generator or vice versa. The resultant 90 phase degree displacement between the two outputs may be achieved by other means, such as for example, by inserting a 90 degree delay line in one of the outputs. The 90 degree phase relationship in all -cases may be monitored by the phase indicator 2l; The phase indicator 21 may consist of a detector and a conventional com-v parator circuit operating to indicate proper phasing to provide equal magnitudes of the frequencies fl and f2. In order to maintain the percentages of modulation nearly constant and to prevent @ver-modulation, -both the amplifier 24 and side band generator 25 may be equipped with automatic volumn control. In addition, the sub-carrier amplifier and the sub-carrier side band generator may be equipped' with negative feedback circuits or other electronic means for accurately stabilizing their outputs.

The outputs of the circuits 24 and 25 are applied to opposite terminals of a sub-carrier bridge 28. The sub-carrier bridge 28 combines the fl and f2 modulated sub-carrier and sub-carrier side band energy and applies the resultant energy to modulate the frequency multipliers I3 and I4. A reversal is included in one arm of the subcarrier'bridge 28 so that energy from the subcarrier side band generator is delivered to the two sides out of phase, while energy from the modulated sub-carrier amplifier 24 is delivered in phase. This produces the sub-carrier modulated localizer `pattern already discussed Wherein antennae 29 and 30 transmit equal amounts of carrier, sub-carrier, and sub-carrier side band q energy. Upon subsequent reception in a mobile frequencies such as fI and-f2, are impressed on craftffthe subi-carrier frequency maybe recovcreda-s if itwere directly radiated by the carrier Both the sub-carrier stages, instead of being transmitted in the form of side band energy. All of the sub-carrier frequencies cary with them the fl and f2 side bands which may be detected in the receiver and used to operate a course indicator.

While we have described above the principles `of our invention in connection with specific apparatus `(and particular modifications thereof), it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of our invention.

We claim:

l. A radio beacon for guiding a craft along a given course comprising iirst and second radiators each mounted on opposite sides of said course on a line normal thereto, a source of carrier radio frequency energy, a source of sub-carrier radio frequency energy, said radiators being spaced Iapart a plurality of wavelengths at said carrier frequency and a fraction of a wavelength at said sub-carrier frequency, means for modulating said carrier energy with said sub-carrier energy, means for applying the sub-carrier modulated carrier frequency energy of different phase to each of said radiators, whereby there is produced an energy pattern effectively defining said course, a source of low frequency energy, and means for further modulating the energy supplied to said first and second radiators with said low frequency energy.

2. An arrangement as set forth in claim 1, wherein said carrier frequency energy source comprises two outputs, means for separately modulating each of said outputs with said subcarrier frequency enengy before application to respective radiators.

3. An arrangement as set forth in claim 2, further comprising means for -causing the frequency of one of the carrier energy outputs to differ incrementally from the frequency at said other output before modulation by said sub-carrier frequency energy.

4. An arrangement as set forth in claim 3, wherein said means for further modulating comprises means for modulating said sub-carrier frequency energy with said low frequency energy.

5. An arrangement as set forth in claim 4, wherein said low frequency enengy comprises energy of a first and second distinct frequency, said sub-carrier frequency energy source comprising two outputs, means for separately modulating each of said sub-carrier frequency outputs with both of said low frequency waves of given phase, and means for separately modulating separate ones of said carrier frequency outputs with sepiarate ones of said modulated sub-carrier frequency outputs.

6. An arrangement as set forth in claim 5 further comprising means for providing a phase displacement between each of said modulated sub-carrier outputs before Iapplication to respective radiators to provide said sub-carrier modulated carrier frequency energy of different phase.

'7. An arrangement as set forth in claim 6 wherein said phase displacement comprises a 90 phase displacement.

8. An arrangement as set forth in claim 7, wherein said means for modulating said subcarrier frequency output comprises means for modulating one of said sub-carrier frequency outy puts with a'rst and second low frequency wave of a given phase, and means for modulating the other sub-carrier frequency output with la first 9. An arrangement as set forth in claim 8, wherein one of said sub-carrier frequency outputs comprises `a sub-carrier frequency amplifier, and

outputs. f' 11. A radio beacon for guiding a craft along a course corresponding to a landing runway comprising first and second radiator means mounted on opposite sides of said course at points substantially opposite the normal point of contact for landing craft, said radiator means being spaced apart a plurality of wavelengths at a principal operating" radio frequency, and a fraction of a wavelength at a second radio frequency, sources of distinctive low frequency signals, and means for applying separate portions of energy at said principal operating frequency modulated with said second frequency and distinguished by said distinctive low frequency to each of said 'radiator means to produce an energy pattern effective in a receiver to produce a course signa indication.

l2. A radio -beacon for guiding a craft along a course comprising first and second radiators Vmounted on opposite sides of said course, said radiators being spaced apart a plurality of vWave- .lengths at the principal operating radio |frequency, means for supplying energy at said principal operating frequency to said first and second radio radiators, a source of energy having a second frequency such that the spacing of the radiators represents a fraction of a wavelength at that frequency, means for separately modulating the energy supplied said rst and second radiators with energy of said second frequency of opposite phase. a source of separate distinctive low frequency signals, and means for further modulating the energy supplied said first and second radiators with said distinctive low frequency signals, whereby there is produced a modulated high frequency energy pattern effective in a receiver to produce a course signal indication.

13. A radio beacon for guiding a craft along a course corresponding to` a landing runway comprising first fand second radiators mounted on opposite sides of said runway at points substan- `from the frequency at said first radiator, a source of energy having a second radio frequency such that the spacing of the radiators represents a fraction of a wavelength at that frequency, means for separately modulating the energy supplied said first and second radiators with energy of said second frequency of opposite phase, a source of distinctive low frequency signals, and means for further modulating the energy supplied said rst and second radiators with said distinctive UNITED STATES PATENTS 10W frequency signals, whereby there is produced Number Name Date a modulated .high frequencyenergy pattern ef- 1,942,162 Shanknn Jan 2J 1934 fectve in a receiver to produce a course signal 2 144 203 shankln Jan 17 1939 indication 5 2288315 Luck LQ- July 7 1942 SIDNEY-B PICKLES- 2,289,899 Bond .my 14, 1942 CHESTER B- WATTS' JR- 2,433,351 Earp Dec. 3o, 1947 REFERENCES CITED FOREIGN PATENTS The following references are of record in the 10 Number Country Date le 0f this patent: 156;338 Great Britain NOV. 11, 1936 

